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UNIX  KRSri  V  OF  ILLINOIS  BL  LLETIN 

ISSUED     W  E  E  K  I   ^ 

\<)l.    XI.  Jl'I.^'  MK    1414.  No.   47 

[Kntered    as    second-class    matter    Dtceinher    11,    1912,    at    tlie    post    office    at 
Urbana,   Illinois,   under  the  Act  of  Aug^ust  24,    1912.] 


BULLETIN  No.  23 
DKPART.MENT  OK  CKRA.MICS 

R.   T.    STULL,    Acting  Director 


NOTES   ON   THE   DEVELOPMENT  OF  THE 
RUBY  COLOR  IN  GLASS 


BY 


E."^  WILLIAMS 


PUBLISHED  BY  THE  UNIVERSITY  OF  ILLINOIS,   URBANA 


1913-1914 


Authorized   Hcpriiit   from    X'oluinc   X\'I,   19U,   Transaetioiis  American   Ceramic  Society 

NOTES  ON  THE  DEVELOPMENT  OF  THE  RUBY 
COLOR  IN  GLASS 

BY    A.    E.   WILLIAMS 

The  term  "riil)}^  glass"  is  applied  to  red  glass  colored  by 
the  use  of  copper,  gold,  selenium  and  in  some  cases,  flowere  of 
sulphur,  the  color  varying  considerably  in  intensity  and  shade. 
In  case  of  copper,  the  color  varies  from  amber  to  various  shades 
of  reds  to  brown  and  to  opaque  black.  With  gold  the  red  has  a 
rose  tint,  and  selenium  ruby  seems  to  be  a  brighter  red  of  vary- 
ing intensities.  The  red  from  sulphur  is  rather  unreliable,  in 
that  a  uniform  color  is  hard  to  obtain,  and  therefore  only  used 
for  lower  grades  of  glass. 

Copper  and  gold  reds  are  said  to  be  due  to  the  metals  in 
suspension  as  colloids. 

V.  PoschP  describes  the  preparation  of  Purple  of  Cassius 
from  gold,  and  shows  that  the  red  or  the  purple  gold-hydrosol 
may  be  obtained,  depending  upon  the  proper  electrolyte  present. 

Paal  's-  proee.ss  for  the  preparation  of  colloidal  solutions 
shows  that  a  red  or  blue  hydro-sol  of  copper  is  obtained,  depend- 
ing- upon  the  properties  of  the  solutions. 

In  G.  Bredig  V  method  of  producing  colloids  elect rolytically, 
he  obtained  finely  divided  metallic  gold,  dark  purple  in  color, 
when  the  arc  takes  place  under  distilled  water.  If  a  trace  of 
caustic  soda  is  added,  deep  red  color  is  obtained. 

That  copper  and  gold  are  in  the  same  condition  in  glass  as 
in  solutions  is  proven  by  the  use  of  the  ultra-microscope. 

Zsigmondy^  says  that  ruby  gla.ss  will  become  red,  or  remain 
colorless  upon  slow  cooling  according  to  its  quality.  It  will  al- 
ways remain  colorless  on  chilling,  the  normal  red  color  generally 
being  brought  out  upon  reheating  to  the  softening  point;  (high 
lead  glasses  show  yellow  or  brown  instead  of  red).  The  coloring 
is  due  to  the  gold,  which  is  at  first  homogeneously  dissolved  in 


1  V.   Poschl,    Chemistry  of  Colloids,  p.    55. 

2  Ibid,  p.   6G. 

3  Ibid,  p.  67. 


2  DEVELOPMENT  OP  RUBY  COLOR  IN  GLASS 

the  g-lass,  later  separatir.g  out  in  the  form  of  ultra-microscopic 
particles  which  reflect  green  light. 

He  compares  this  phenomenon  with  devitrification,  and  re- 
fers to  Tannnann's'"^  work  on  de^^tritieation.  Tammann  shows 
that  the  speed  of  crystallization,  and  the  ability  to  crystallize  in- 
crease with  diminishing  temperature  from  the  melting  point  and 
then  decrease  again,  while  viscosity  steadily  increases.  Zsig- 
mondy  applies  Tammann 's  results  to  ruby  glass  in  this  manner: 

"Ruby  glass  is  worked  several  hundred  degrees  lower  than  its 
melting  temperature.  At  the  working  temperature,  conceive  it  as  a 
super-saturated  crystalloid  solution  of  metallic  gold  and  the  smallest 
amicroscopic  particles  to  be  centers  of  crystallization,  it  will  at  once 
be  seen  why  ruby  glass  sometimes  remains  colorless  upon  simple 
cooling.  In  this  case  tlie  optimum  temperature  for  spontaneous 
crystallization  is  so  low  that  the  glass  is  very  viscous  and  the  speed 
of  crystallization  reduced  to  a  minimum.  If  by  reheating,  the  glass 
acquires  a  certain  mobility,  the  gold  separates  out  upon  the  nuclei 
present  which  by  growth  become  sul)-microns,  visible  in  the  ultra- 
apparatus  and  turning  tlic  glass  red  or  darker." 

V.  Poschl''  says  that  gold  ruby  is  obtained  by  an  addition 
of  gold  chloride  to  the  glass  melt  from  which  particles  of  gold 
separate  out,  when  the  mass  is  quickly  cooled.  These  particles, 
however,  have  the  magnitude  of  amicrons,  so  that  the  glass  ap- 
pears colorless.  By  heating  anew  until  the  glass  becomes  soft, 
the  particles  grow  until  they  attain  the  size  of  ultra-microns,  to 
which  the  cause  of  the  red  color  is  traced.  The  preparation  of 
copper  ruby  glass  is  performed  by  an  analogous  method. 

Copper  ruby  has,  in  the  past,  been  made  by  a  process  known 
as  flashing.  Tliis  process  is  described  somewhat  as  follows  by 
Rosenhain :" 

"Flashing  glass  is  the  process  of  placing  a  very  thin  layer  of 
colored  glass  on  the  surface  of  a  more  or  less  colorless  glass  of  usual 
thickness.  This  is  generally  accomplished  by  taking  a  small  gather- 
ing of  the  colored  glass  on  the  pipe,  and  the  remaining  gathering  for 
the  piece  to  be  made  from  the  colorless  glass  pot.  When  this  glass 
is  blown,  the  ruby  glass  lies  in  a  thin  layer  over  the  inner  surface  of 
the  cylinder.  The  special  skill  required  is  in  blowing  this  layer  to  a 
uniform  thickness  to  obtain  a  uniform  color." 

*  Ztiprmondy,  Colloids  and  the  ultia-mirroacopc,  p.   16.'). 

=  Taii.nianii.   Ziit.    for   Electro-chcmi,    1904,    Vol.    10,    p.    532. 

«Ibid  I,  p.   103. 

'  Waltrt    Ros^-^^hain,   Glass   Manufacture. 


DEVEI-OPMEXT   OF   RUBY    COLOR   IX   (JLASS  3 

The  necessity  of  flashing-  is  tliic  to  tJlie  density  of  the  coloi-. 
Cop})er  coUns  are  so  dense  that  many  ylasses  are  opaque  when 
over  3  ni.iii.  tliiek,  the  eolor  depending  ni)on  tlie  e-(inipt)sitit)n  and 
rate  of  eooling.  However,  it  is  p()sNil)h'  to  control  tlie  density  of 
the  ec>h>r  somewliat  in  the  Hashed  i-uby  glass  by  carefully  eon- 
trolling-  the  temperature  of  worldng  the  glass  and  rate  of  cooling 
in  the  moldis. 

These  factors  nuust  be  controlled  very  carefully  in  praccice 
to  produce  uniform  results.  If  these  gkisses  are  cooled  very 
quiekly,  as  for  instance,  chilling  in  water  or  rolling-  very  thin 
(2  ni.m.  thick)  on  an  iron  plate,  the  red  coloa*  will  not  develop, 
01'  at  least  shows  only  in  scattered  streaks.  By  reheating  at  defi- 
nite temperatures,  the  color  miay  be  obtained  in  varying  degrees 
of  intensity  from  aml)er  to  opaque  black,  dei)ending  upon  the 
temperature  to  which  the  glass  is  reheated.  Thus  it  will  be  seen 
that  the  temperature  and  rate  of  cooling  nnist  l)c  constant,  to 
I^roduce  a  unifoi-m  shade  of  red  when  this  color  is  developed 
during  blowing. 

At  the  present  time,  howevei",  copper  ruby  glass  is  being- 
made  in  which  the  color  does  not  come  out  in  the  pressing  or 
working,  but  is  brought  out  later  by  reJieatiug.  The  density  of 
the  color  in  this  glass  is  very  much  less  than  the  Hashed  rul)\- 
glass,  and  pieces  of  greater  thickness  can  be  easily  made.  The 
eolor  range  from  a  light  amber  through  reds  to  a  dense  opaque 
bliaek.  with  an  increasing  temperature. 

Available  literature  consulted  (ui  the  subject  gdve  no  eom- 
])lete  or  definite  methods  foi-  woi-l<ing  i-nby  glass,  but  emphnsized 
the  necessity  for  care. 

The  following  are  some  fornudae  and  directions  obtained : 

Gerner,-'^  gives  a  history  of  copper  ruby  glass  and  a  number 
of  mixes  with  methods  of  handling.  The  following  are  two  of 
the  bat-ches  given  hv  him  : 


^  (Icnicr,    ••'■.'/rtss,-'   p.    19.'> 


DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 


GERMAN   COPPER  GLASS 

.     100.0  Sand 

25.0  Potasli 

17.0  Borax 

2.5  CU2O 

5.0  SnOo 

0.2  Fe.Oa 

2.5  MnO. 

0.5  Bone  ash 


Calculated   Formula^ 


0.200  PbO 
0.390  K.O 
0.120  Na,0 
0.095  CuO 
0.079  MnO 
0.01-4  CaO 


0.0060  FeA 
0.2500  B063 
0.0044  P.,0. 


4.3G  SiO, 
'0.09  Slid., 


100  SiO_, 

50  Pb;X), 

25  KXO, 

5  NaNO, 


FRENCH   COPPER   GLASS 

'J'liis  hatdi  is  fiuscd,  c'lliilled,  dried,  ground 
and  iiiixod  with  1  CuJ),  1.5  SnO.,  5  cream 
of  tartair.  This  is  incited  and  hhisted  one 
hnuf  duriiiii'  melt. 


Calculated   Formula 

0.534   PbO 
0.346  K.O 
0.074  Na,0 
0.046  CuO 


3.900  SiO, 
0.034  SiiO., 


Notes  on   ruby  gbus.s  from  SpreohsaiaP"  give  the   following 
by  translation : 

"In  the  manufacture  of  ruby  glass  it  is  not  in  the  field  of  the 
furnace  man  to  control  the  color.  Repeated  fusion  and  cooling  makes 
the  best  color,  and  the  color  does  not  depend  as  much  upon  the  per- 
cent of  coloring  oxide  in  the  mix  as  upon  the  temperature  of  the 
glass  while  working,  the  rate  of  fusion  and  rate  of  cooling  the  fin- 
ished piece."     The  following  batch  is  given: 


"The   empirical    formulae   of   all    fflasses   Riven    in   the   follnwint;    work   were   calculated 
l)v   the  writer. 

^"  Sviechsaal,  Feb.   6,    1913,  p.    92. 


DEVELOPMENT  OF  RVBY    COLOR  IX  CLASS  D 

I.KillT    HKI)  HARK    RED 

Sand     100.0  kg.  100.0  kg. 

Soda    ash    IG.O  kg.  16.0  kg. 

Potash     IC.o  kg.  IG.O  kg. 

Borax     4.0  kg.  6.0  kg. 

Whiting    10.0  kg.  12.0  kg. 

Witherite    10.0  kg.  10.0  kg. 

CiuO     2.0  kg.  4.0  kg. 

SnO.     2.0  kg.  4.0  kg. 

Fe.O.    0.5  kg.  1.0  kg. 

Cream    of    tartar 0.8  kg.  1.15  kg. 

Calculated    Molecular  Formula 


0.385   X;i,()   j 
0.210  K,0 
0.222  CaO 
0.110  BaO 
0.0H4  CnO 


0.0066  FeX).,   )3.63  SiO, 
0.0660  B.,()..   10.03  SnO., 


"Tlic  manufacture  of  ruljv  glass  demands  great  care  and  practice 
in  working.  This  is  especially  so  with  pressed  glass.  The  raw  l)atch 
should  be  put  into  a  preheated  pot  and  melted  six  hours.  The  melt 
is  blasted  several  times  and  poured  into  cold  water  for  remelting  and 
refining.  If  the  pressed  pieces  are  not  colored  enough  they  can  be 
reheated.  The  mold  must  not  be  too  hot  to  allow  the  glass  to  cool 
too  slowly,  or  too  cold  to  chill  and  cause  the  pieces  to  crack.  The 
following  batch   is  also  given:"" 

Sand     100.0  kg. 

Potash     25.0  kg. 

Red    lead    25 . 0  kg. 

Borax    10.0  kg. 

Soda     5.0  kg. 

Cu.O    3 . 5  kg. 

SnOc    2.0  kg. 

Fe.O.,    0 . 5  kg. 

MnO.     0.5  kg. 

Gullet     25.0  kg. 

Cream    of   tartar    0.5  kg. 


Ibid    1(1,   l>.    '.)■!. 


DEVELOPilEXT    OF    RUBY    COLOR    IX    GLASS 
Calculated    Molecular    Formula 


0.2020  K,0 
0.6230  PbO 
0.1010  Xa.O 
0.0668  Cn'o     ! 
0.0079  MnO 


0.00418  Fe,0,     I  2.310  8i0, 
0.07250  B.,6,         0.018  SnO, 


Rudolf  Ih)lill)aum^-  says  that  red  colors  may  be  obtained  by 
tlie  use  of  CuoO,  selenium,  sulphur  and  gold,  but  is  most  often 
obtained  from  Cu.O.  He  gives  the  following  hatch  for  a  copper 
ruby : 

100.0  SiOo 
34.0  KXO3 
16.0  CaCO,  K,CO3=80  to  85  percent  pure 

0.6  Cu.O 

2.0  Snb, 

Calculated   Formula 
0.536  K.,0  1     .   -r-f.  c?.^ 

ll()hll)aum  says : 

"Concerning  the  mixing  of  the  Cu^O,  I  wish  to  remark  that  it  is 
possible  to  obtain  the  ruby  color  with  0.4  percent  Cu;0,  also  with 
0.8  percent.  However,  with  0.8  percent  of  the  batch  as  CueO  the  color 
is  so  dense  that  large  masses  are  not  workable.  As  such  a  small  quan- 
tity of  Cu:0  is  needed  to  make  ruby,  it  is  mixed  best  by  using  0.8  per- 
cent CuoO  and  SnO  with  half  the  batch  of  glass.  When  the  glass  is 
ready  to  blast  then  mix  the  batch  containing  0.8  percent  Cu:0  with  an 
equal  batch  of  crystal  glass,  and  a  0.4  percent  CU2O  batch  is  obtained 
which  gives  a  weaker  color.  It  is  best  to  employ  SnO  as  a  reducing 
agent  to  insure  the  obtaining  of  a  ruby  color,  and  one  finds  from 
practical  experience  that  the  mix  must  contain  less  than  double  the 
quantity  of  Cui:0  as  SnO.  If  this  is  not  sufficient  reducing  agent, 
cream  of  tartar  may  be  used  in  quantities  to  satisfy  all  conditions. 
Iron  scale  may  also  be  used  as  a  reducing  agent  but  the  pure  ruby 
color  is  then  changed." 


'- R.     liohlbaimi,    Siitffeirassi    Ilerstellunff    lieaibdtung    vi.d    Verziervng    des    Felnern 
liulglasfs,   p.   125. 


DKVKLOI'.MKXT    OF    RUBY    COLOR    IN    GLASS  7 

llolilhauiii'-  gives  the  foll<»\viii-i'  hiitrli  for  a  gold  ruby: 
Rose  Color 

Sand     100.0  kg. 

Potash     .'54.0  kg. 

Calcium    carimnatc     \7 .0  kg. 

Gold     l''-0  yms. 

Gold  must  ht'  l)l•ou^ht  into  tlie  mix  in  ii  very  finely  separ- 
ted  form,  best  in  solution  or  as  Purple  of  Cassius. 

To  i:et  the  gold  in  solution,  it  must  be  cut  into  small  pieces 
and  dis.solved  with  acjua  regia.  The  gold  solution  is  poured  on 
part  of  the  mix.  and  this  mixed  with  the  l)alaiiee  of  the  batch. 

In  the  heat  of  the  oven,  the  decomposition  of  the  go:d 
chloride  takes  place  so  rapidly,  that  a  portion  of  the  gold  chlor- 
ide is  carried  away  nndeeomposed.  There  is,  therefore,  not  so 
much  gold  dissolved  in  the  glass  as  is  introduced,  and  the  color 
is  much  weaker  than  it  would  be,  if  all  the  ,^old  were  dissolved. 
It  is,  of  course,  reasonable  for  one  to  try  and  reduce  the  vapori- 
zation of  the  gold  chloride  as  much  as  possible.  This  may  be 
done  by  pouring  the  gold  chloride  on  1  kguL  of  sand  and  evap- 
orating to  dryness.  Then  mix  this  well  with  half  of  the  batch, 
or  iLse  gold  purple  in  the  same  nuinner. 

According  to  Hohlbaum's  experience,  either  phosphoric  acid 
or  ])ari\nn  work  favorably  in  the  making  of  gold  ruby,  causing 
the  gold  to  separate  out  more  rapidly.  Without  either,  the  ruby 
is  too  light.  A  batch  for  making  a  rose  glass  wdth  a  violet  tinge 
with  the  nse  of  barium  is  given. 

Rose   Glass   with   Barium 

Sand    100.0  kgm. 

BaCOa    16.0  kgm. 

95  percent    soda,    Na-CO. 4.'?.0kgm. 

Gold    12.0  gms. 

Selenium  Ruby,  Light  and  Rose  Colored 

Arsenic     200.0  gms. 

Sand     100.0  kgm. 

Potash.   80-85   percent    ,'54.0  kgm. 

CaCO.    17.0  kgm. 

Selenium    nitrate     120.0  gms. 

"  ll.id    12.    |).    12G. 


8  DEVELOPMENT  OF  RUBY  COLOR  IX  GLASS 

In  the  reds  with  sulphur,  one  should  not  use  the  alkali  sul- 
phates, but  only  sulphur  with  charcoal  as  a  reducing  agent.  The 
charcoal  keeps  the  sulphur  from  conil)ining  with  the  soda  and 
potash.  In  sulphur  ruby,  a  great  part  of  the  sulphur  vaporizes 
in  the  working.  The  melting  glass  foams  vigorously,  and  there- 
fore one  should  fill  the  pot  only  half  full  at  first,  and  after  the 
batch  reaches  quiet  fusion,  put  in  the  second  half. 

Sulphur  ruby  is  hard  to  make  in  uniform  coloi*s.  and  dark- 
ens in  the  nuiffle.  It  is  not  used  for  nuikiug  higher  grades  of 
glass.     Two  batches  for  sulphur  i-uby  are  given  : 

No.  1  No.  2 

Sand    100 . 0  kgm.  100 . 0  kgm. 

Soda    45.0  kgm.  45.0  kgm. 

CaCOs     20.0  kgm.  20.0  kgm. 

Flowers    of   sulphur    T.okgm.  10.0  kgm. 

Antimony    sulphate     5.0  kgm. 

Charcoal    2.0  kgm. 

EXPERIMENTAL    DATA    BY    WRITER 

The  foregoing  typical  batches  for  ruby  glass  are  but  a  few 
of  a  large  numl)er  given  in  the  literature  pertaining  to  glass 
making.  An  examination  of  these  shows  a  wide  variation  in  com- 
position, but  all  agree  in  that  they  ai-e  high  in  silica  and  contain 
tin.  In  copper  ruby,  the  amounts  of  c()pi)ei'  and  tin  vary  widely 
in  their  ratios  to  each  other.  These  copper  rubies  are  probably 
u.'-ed  in  the  manufacture  of  tlashe<^l  glass. 

In  the  beginning  of  the  following  experimental  work,  sam- 
ples of  conniiercial  copper  ruby,  both  the  quick-cooled  colorless 
and  ruby  colored  were  obtained.  The  uncolored  sample  was 
broken  into  fragments,  and  different  fragments  were  heated  to 
different  temperatures  for  various  lengths  of  time.  A  small 
Iloskins  electric  furnace  was  used,  and  temiperatures  were  read 
with  a  Leeds  Xorthiiip  potentiometer,  using  a  platinum,  plati- 
num-rhodium thermocouple. 


DEVELOPMENT    OF    RI'BY    COLOR    IX    GLASS 

The  followinoj  results  were  obtained : 


PIECE 

MAXIMUM 
TEMPERA- 

TIME     HELD 
AT       MAX. 

REMARKS 

NO. 

TURE 

TEMP. 

°c 

minutes 

1 

500 

30 

No   change   in   color 

2 

500 

60 

No  change  in  color 

3 

550 

30 

No  change  in  color 

4 

550 

60 

No   change   in   color 

5 

575 

1 

No  change  in  color 

6 

575 

30 

No  change  in  color 

7 

600 

1 

\'ery  light   amber 

8 

600 

15 

\'ery  lig"ht   amber 

9 

600 

30 

Brig-ht  amber,  sHg-htly  darker 
than   No.  8 

10 

600 

60 

Bright   amber,    same   as   No.   9 

11 

650 

1 

Bright   amber,    same   as    No.   9 

12 

650 

30 

Deep  ruby,  edges  slightly  soft- 
ened 

13 

650 

60 

Same  as  No.  12,  edges  slightly 
softened 

14 

675 

15 

Same  as  No.  12,  edges  slightly 
softened 

15 

675 

30 

Same  as  No.  12,  edges  slightly 
softened 

16 

675 

60 

Darker  than  No.  15,  edges 
slig-htly   softened 

17 

700 

1 

Same  as  No.  10,  edges  slightly 
softened 

18 

700 

30 

Dark  red,  edges  slightly  softened 

19 

900 

30 

Grayish  purple,  opaque,  softened 
out  of  shape 

The  rate  of  increase  of  temperature  was  a  constant  factor 
in  all  of  these  tests,  as  follows :  ten  minutes  from  room  tempera- 
ture to  300° C;  300° C  to  500° C  at  rate  of  50°  per  minute;  500° C 
to  maximum  temperature  at  a  rate  of  25°  per  minute. 

The  results  seem  to  show  that  the  color  at  any  definite  tem- 
perature is  practically  constant,  and  that  the  color  chang-e  at 
that  temperature  is  apparently  instantaneous.     However,  time  k 


10  DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 

required  for  the  temperature  to  even  up  through-out  the  thick- 
ness of  the  piece. 

It  will  be  noticed  that  the  glass  shows  signs  of  softening 
at  that  temperature  at  which  the  strong  color  develops.  This  is 
probably  the  softening  point  Zsigmondy^^  refers  to  in  the  article 
pre\dously  quoted.  It  is  observed  that  there  is  little  or  no  ap- 
parent change  in  color  brought  out  between  650°  and  675°,  giv- 
ing a  safe  range  for  an  annealing  oven. 

Most  of  the  glass  fornnilas  observed  were  high  in  lead  and 
in  silica.  Accordingly  the  following  formuia  was  selected,  it 
being  the  upper  silica  limit  for  most  glasses : 

0.5  PbO      I    .,  ^.^ 
0.5  Xa.O    }   '  ^^^^ 

In  order  to  determine  a  suitable  iiietliod  of  working,  several 
small  batches  of  this  glad's  were  fused.  The  inetliod  adopted  was 
as  follows : 

The  glass  was  fused  in  Battersea  crucibles  in  a  small  pot 
furnace  using  gas  and  compressed  air.  The  temperature  range 
required  for  firing  and  to  make  the  glass  liquid  enough  for  pour- 
ing, was  between  1480  C  and  1520  C.  One-half  hour  was  taken 
for  complete  fusion  of  the  lead  glasses  and  one  ht)ur  for  the  lead- 
less  glasses. 

Not  much  trouble  was  experienced  in  reducing  the  copper 
oxide  ami  preventing  oxidation.  Although  a  slight  reducing 
flame  was  used,  the  presence  of  cream  of  tartar  ^al)r)ut  '^  per- 
cent) seemed  to  make  reduction  certain,  if  the  time  of  heating 
was  not  too  long. 

When  fusion  was  complete  the  gla.ss  was  poured  on  a  heavy 
cast  iron  plate  1  in.  thick,  and  then  rolled  to  a  thickness  varying 
from  2  to  5  m.ni.  The  thinner  portions  usually  cooled  colorless, 
and  the  color  developed  in  the  thicker,  .slower  cooled  portions, 
i.  e.  turning  red  or  opaque  brown  or  black. 


"Ibid    4. 


DEVEI.Ol'MKXT    OF    HrHV    COLOR    IX    GLASS 


11 


c  c  s  o  cJ  t^  o 

o  c  o  o  o  o  o 

in  or  CJ  O  O  O  '" 

o  o  o  c^  o  c  c; 


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>n  re  01  o  o  c  '" 

o  c  o  r-  o  o  s 


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12  DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 

SERIES  A 

Glass  batches  were  then  made  corresponding  to  the  for- 
mulas given  in  Series  A. 

The  following  results  were  obtained: 

Number  1  — Colored  out  vei*y  dense  opaque  grayish-brown 
color. 

Number  2— (Decreasing  the  coloring  agent.)  This  poured 
well,  and  cooled  practically  coloiless  at  5  m.m.  thick.  Softened 
out  of  shape  at  675°C.  ar.d  colored  out,  streaked  with  reddish 
color.  At  700°C.  it  beeime  dnrk  l)rown.  (>pa(iue  and  still 
streaked,  very  soft. 

Xumber  8— (Irc:e:!sii  g  tin  to  harden.).  This  poui'ed  well 
and  was  colorless  except  i'nr  a  pnle  giH'enish-yellow  coh)r  at  5 
iii.ni.   thick. 

Heated  to  480 "C,  gives  amber  coloi'. 
Heated  t'>  525° C,  gives  deep  red  color. 
Heated  to  700° C,  softened  out  of  shape  giving  a  dense, 
brown  opaque  glass.     Color  change  very  rapid. 
Xumh.'r  4— (Uecren.sing-   the    Cu.O   to   reduce   intensity   of 
color).     Color  developed  darker  !han  No.  :}  in  ])nnring,  having  a 
greenish  cast.     Heated  to  600-C.  its  culo!'  was  deep  opaque,  and 
neai-ly  black,  aiiihei-  at  550°C.,  and  hrown  at  575°C. 

Xuiiiher  5— Developed  a  ralhei-  intense  bi'own  color  while 
pouring.  Thin  colorless  sections  gave  a  deep  greenish  l)i'nwn  at 
550"  C.  and  a  dense  opaque  black  at  600° C. 

Xumber  6— (Still  reducing  airount  of  coloring  matter). 
This  glass  poured  clear  and  colorless.  On  reheating  it  changed 
to  opaque  black  from  550° C.  to  600° C.  Color  change  very  rapid. 
Xuiid)er  7— (Coloring  matter  left  out  to  test  purity  of  ma- 
terials for  iron).  This  glass  on  reheating  at  various  temi)era- 
tures  gave  no  change  in  color. 

The  conclusions  from  this  series  of  glasses,  (excluding  No. 
1)1^'  are: 

(1)     Low  amounts  of  copper  seemed  to  increa.se  the  density 


'■■^  Tliis   slass   \v;is   not    nioltrd   well   enough    to    jiKlge   results. 


DE\'EI.OPMKNT    OF    RUBY    COLOR    IX    GLASS  13 

or  oi)aeity  of  the  colof,  ar.d  decreas-e  the  signs  of  red,  giviii<i; 
greenish  browns. 

{'2)  An  increase  in  the  tin  in  No.  ;}  si  !pi)ed  the  streakiness 
shown  in  No.  2. 

(3)  (ihiss  Xo.  '^  was  the  l)est  glass  in  series  A,  giving  a 
eohiress  glass  wlieii  poured  and  eooled  (iniekly.  Reheating 
shiiwed  shades  of  good  red  at  various  te;iii)eraf ui'cs.  However, 
the  color  change  is  so  rapid,  it  wnuhl  he  difliiMilt  1o  contrnl  uni- 
formity of  color. 

SERIES  Al 

Sei'ies  Aj  was  eoiistrueted  in  order  io  obtain  harder  glasses 
tlian  tliose  in  series  A,  by  replacing  PbO  with  CaO  so  as  to  raise 
their  temperatures  of  softening,  and  t;T  determine  how  this  af- 
fects the  range  of  color  change. 

Glass  Xo.  1  of  this  series  showed  a  dark  brandy  color  on 
pouring,  coloring  out  quicker  than  Xo.  3  series  A.  which  con- 
tained the  same  etjuivalents  of  Cu  and  Sn.  This  glass  did  not 
soften  out  of  shape  on  reheating  at  700° C,  as  did  glass  No.  3, 
series  A,  but  gave  a  dense  opacine  color.  If  it  could  be  handled, 
without  coloring  in  pressing,  this  glass  gives  a  good  transparent 
red  at  5  m.m.  thick,  upon  reheating  to  the  proper  temperature. 

Glasses  Nos.  2  and  3  (reducing  Cu^O).  Colored  out  quite 
dense,  on  pouring  becoming  nearly  opaque.  When  reheated 
above  600° C.  the  glass  turned  a  deep  opaque  purple. 

Glass  No.  4  (reducing  SnOo).  This  glass  seemed  to  color 
out  as  rapidly  as  Nos.  2  and  3. 

The  conclusion  which  may  be  drawn  from  this  serias  is  that 
the  rapidity  of  precipitation,  or  growth  of  color  is  increased,  in- 
stead of  decreased,  as  would  be  expected  by  hardening  the  glass. 

SERIES  B 

The  l)asal  formula  for  this  series  is  one  of  the  published 
fornudas  given  in  Sprechsaal.^'^  It  is  a  high  lead  low  silica 
glass,  containing  some  borax  and  is  a  nmch  softer  glass  than 
series  A  and  Al. 

"■•  Ihifl    10. 


14 


develop:ment  of  ruby  color  in  glass 


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DEVELOPMENT  OF  RUBY  COLOR  IX  OLASS  15 

The  results  showed  this  very  inarkciUy.  The  fusions,  luade 
at  the  same  temperature  range  1480  ("  and  l.l'JO  (',  were  more 
fluid  and  poured  easier. 

Numbers  1.  2,  3  and  4  developed  deej)  oijatpie  glasses  when 
poured  4  to  -■)  m.m.  tliiek.  The  thinner  portions,  however,  in- 
creased in  degree  of  transparency  to  about  2  iilul  at  which 
thickness  the  glasses  cooled  colorless,  but  of  course  very  l)rittle. 
Upon  reheating,  the  colorless  pieces  of  these  four  glasses  colored 
to  about  the  same  color  density  \vh<?n  heated  to  the  same  tem- 
perature. At  500  C,  they  showed  an  amber  color  changing  to  a 
light  red  at  525°C.,  and  to  a  ruby  color  at  550°C.,  becoming 
opaque  at  600° C.  Leaving  out  the  iron,  or  manganese  or  both, 
(especially  the  latter),  seemed  to  improve  the  (luality  of  the  red 
and  to  give  a  less  dense  color.  This  type  of  glass  gives  a 
much  better  red  color  than  any  of  series  A,  but  it  is  impossible 
to  work  with  sections  as  thick  as  commercial  g'.ass  pieces  would 
be  made  and  still  obtain  a  transparent  color.  However,  it  would 
work  as  a  ruby  glass  in  making  tiashed  articles  and  give  a  good 
color.  ]\langanese  dioxide  and  Fe.O;,  are  detrimental  rather 
than  heljjful  in  obtaining  good  colors. 

In  series  B,  Numbers  5,  6  and  7  (in  which  SnOo  is  absent), 
the  glasses  were  more  opaque  in  all  cases.  Number  7  colors  out 
even  in  the  thin  sections  to  a  dense  black. 

In  glasses  Nos.  8,  9.  10,  11  and  12.  the  tin  was  kept  constant 
and  the  copper  varied.  In  all  cases  the  tendency  was  to  increase 
opacity  and  the  rapidity  in  which  the  color  appeared  on  pouring. 

In  glasses  Nos.  13.  14  and  15,  in  which  the  tin  was  increased, 
no  beneficial  results  were  obtained,  since  these  glasses  were  more 
opaque  than  the  preceding  ones  in  the  group. 

The  rub}'-  color  in  glasses  as  soft,  and  as  low  in  SiOo  as  the 
members  of  this  group  cannot  be  controlled.  However,  when 
Bl  and  B2  were  melted,  (|uenched  in  water  and  remelted,  there 
was  an  improvement,  since  all  signs  of  streakiness  disappeared, 
and  the  color  became  verv  uniform  on  reheating. 


16 


DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 


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DEVELOPMENT    OF    RIBV    COI.OH     IN    GLASS  17 

The  hii.sis  ol"  this  sci'ics  obtaiiitnl  from  1  Inhlliauiii' '  is  eii- 
tii-ely  dilVri'i'iit  than  sri'ii's  \i.  It  is  a  liiiie-potfish.  hijjch  silica, 
leadk-.»s  ghuss,  with  lii^h  tin,  tiuTt'l'ore,  a  coniparatively  refrac- 
tory and  viscous  jrlass  at  l!)\v  tc:i:peratiii-i's.  One  hour  was  taken 
for  fusion. 

Iloldbaum's  hatcli  calls  for  SiiO  as  thi^  I'eilucing  aiz;ent, 
cream  of  tartar  hein«r  atlded  as  a  prccaiiiioii  to  insure  sufficient 
reduction.  Nuiiihci-  C-l  was  first  made  hy  suhstitution  of 
SnO^,  for  SnO,  antl  leavinji  out  the  ci'eam  of  tai'tar.  An  oxidized 
clear  colorless  p'lass  was  the  result,  uivin^'  no  color  change  when 
reheated  beyond  tlie  softeiiin*;-  point. 

Xunil)er  C'-I  was  again  made  using  SnO._.  and  0.5  percent 
cream  of  tartar.  This  glass  was  exceedingly  visciuis  and  quickly 
cooled  belo'W  the  jioint  of  easy  jiouring.  Upon  ixtui'ing  and  roll- 
ing, (although  taking  a  little  more  time),  no  coloi-  change  took 
place,  the  glass  remaining  clear  and  coloi-less. 

Upon  reheating,  no  color  change  took  place  until 

8(X)  ('.  was    reached,    when    a    light    amhci-   color   was 

ohtaiiu'd, 
850°C.  gave  a   pale  reddish  brown, 
900° C.  g'ave  a  light  brown, 
lOOO'C.  softened  with  an  opacpic  bi'own  color. 
The  red  color  was  not  good  in  this  glass  and  it  seemed  to  be 
entirely  too  refractory. 

Series  C.  Xo.  2.  (Reducing  SiO.  to  soften).  This  showed 
an  improvement  in  the  working  qualities  \nth  no  tendency  to 
color  out  on  pouring. 

Reheating  this  glass  gave  the  following  residts : 
800° C.  a  distinct  light  red, 
850° C.  a  good  ruby  color. 

900°C.  a  deep   dark   red   nearly   opa(|ue   when   -i   m.m. 
thick. 
Series  C,  No.  3  (reducing  SiO._,  still  further)  gave  a  fusion 
which  poured  colorless  and  flowed  freely.     Reheated  to  850^  it 
showed  a  reddish  brown,  slightly  streaked.     900°  showed  a  dis- 
tinct deep  brown. 

1'  Il>i(l   n.   p.    121. 


18 


DEVELOPMENT    OF    RUBY    COLOR    IN    GLASS 


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DEVELOPMENT  OF  RLBY  COLOR  L\  GLASS  19 

Series  (',  Xo.  4  (less  SiO.  than  L'-i).  Poured  clear  and  col- 
orless l)ut  when  reheated  to  850'  beeame  more  streaked  and 
showed  a  more  decided  brown. 

Series  C,  Xo.  5,  ])oured  clear  and  colorless  as  tiie  others,  but 
showed  brown  streaks.  When  reheated  to  801)"  it  showed  a  very 
streaked  brown  color.  AVlien  the  glass  was  remelted  and  re- 
poured  it  gave  a  very  clear  glass. 

Upon  reheating  this  to  750^C.  the  color  came  out  a  clouded 
black,  increasing  in  intensity  with  the  reheating  temperature. 

The  foregoing  five  glasses  in  group  C  show  that : 

(1)  Reducing  the  SiO.  from  4.57  to  -i.U  molecules  improved 
the  color  in  this  series.  Further  reduction,  however,  changed 
the  color  to  browns  and  then  blacks,  giving  about  the  same  range 
of  brown  and  blacks  with  o  SiO.  as  series  A  gave,  having  3  SiO, 
and  small  amounts  of  copper. 

(2)  High  silica  seems  necessary  in  order  to  develop  a  good 
red  color.  The  color  change  takes  place  at  rather  high  tempera- 
tures for  a  reheating  furnace,  and  the  glass  appears  to  be  too 
viscous  for  good  working  properties.  Glasses  C6,  C7  and  C8 
were  made  by  introducing  PbO  in  place  of  part  of  the  CaO  with 
the  idea  of  softening  and,  if  possible,  still  retaining  the  property 
of  not  coloring  out  on  pouring. 

C6  and  C7  in  which  0.2  PbO  replaced  0.2  CaO  showed  a  dis- 
tinct improvement  in  the  working  cpialities  and  uniformity  of 
color,  although  these  glasses  colored  out  in  the  thicker  portions 
during  the  pouring;  C6  to  a  light  red  and  C7  to  a  deep  ruby. 
Thase  glasses,  however,  were  transparent  to  a  thickness  of  8  m.m. 
in  comparison  with  series  B,  which  were  not  transparent  in 
pieces  over  2V2  m.m.  in  thickness. 

Reheating  clear  portions  of  C6  gave  a  good,  deep,  ruby  color 
at  650°C.,  a  considerable  lowering  of  the  temperature  over  the 
leadless  glasses  for  developing  color.  This  g'ass  also  has  a  fairly 
constant  color  over  a  temperature  range  of  25^ C  (625°  C.  to 
650°C). 

Series  C,  No.  7  colored  out  at  570°  to  the  same  shade  as  C6. 

Serias  C,  No.  8  (Reducing  PbO  to  0.1  with  4.00  SiOJ.  This 
glass  gave   evidences  of  being  harder   than    the   ])rcvious   glass 


20  DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 

(C7)  as  the  fusion  colored  out  a  veiy  little  clearer  at  6  m.m. 
thick  (similar  to  C6),  and  the  color. ess  portions  gave  a  deep 
clear  ruby  on  reheating  to  570'',  the  same  as  C7  and  about  60° 
lower  than  C6.  This  glass  gave  the  clearest  and  best  red  ob- 
tained in  the  foregoing  work. 

Series  C,  No.  9  (in  which  0.1  FbO  was  replaced  in  C8  by 
0.1  XaoO  as  borax)  gave  a  glass  considerably  more  fusible,  and 
flowed  well  in  pouring.  A  very  streaked,  nearly  black,  color  de- 
veloped in  portions  over  3  m.m.  in  thickness  on  pouring.  Thin 
transparent  pieces  heated  to  750^"  gave  a  red  color,  streaked  with 
opacjue  black  lines.  This  fusion,  therefore,  did  not  give  good 
results.  The  po.ssibility  of  spoiling  the  color  by  over-heating  is 
ever  present.  It  is  possible  that  less  BoO.j  would  give  better  re- 
sults, though  this  was  not  tried. 

Series  C,  No.  10  (0.1  Xa,,0  replacing  0.1  L'aO).  The  result- 
ing glass  was  clear  and  colorless,  sliowing  a  very  few  light  red 
streaks.  The  working  properties  of  the  glass  were  very  good, 
especially  in  i)ouring  and  cooling. 

On  heating  to  700  C  the  gla.ss  tui-ned  a  clear  light  red. 
625 ^C.  showed  a  clear  light  red. 
725^0.  showed  a  clear  light  red. 

The  color  range  of  this  glass  is  therefore  good. 

Series  C,  No.  11  (0.1  R)0  replacing  0.1  CaO  and  with  4.57 
SiOJ.  Results  from  this  gla.ss  were  a  failure  as  the  fusion  was 
incomplete  and  very  viscous  and  colored  out  a  dense  opaque 
black  on  ])()uring.  If  i)rop(M'ly  fiisiMl,  liettcr  results  would  no 
.l()ul)t  have  been  obtained. 

Series  C.  No.  12  (0.1  Xa,0  replacing  0.1  CaO  and  with  4.57 
SiOo).  This  glass  gave  a  very  good  fusion,  but  was  rather  vis- 
cous and  showed  no  color  on  pouring.  Heating  this  glass  to 
700' C  gave  an  amber  colored  glass  streaked  with  dark  red  lines. 
At  800°  C  it  showed  a  good  even  ruby  color. 

The  conclusions  from  this  last  series  of  glasses  (C6  to  C12) 
are  (1),  that  soda  replacing  lime  softened  the  glass  without 
causing  the  color  to  come  out  in  cooling.  (2)  Lead  on  the  other 
hand  caused  these  glasses  to  color  out  rapidly  on  cooling,  but 
did  not  make  them  opaque. 


DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS  21 

General  Conclusions.  The  following  are  general  conclu- 
sions one  may  drav;  from  this  work  regarding  the  composition 
of  a  workable  ruby  gla.ss.  A  workable  rul)y  glass  is  one  which 
will  not  color  out  when  cooled  at  the  rate  obtained  in  the  press- 
ing process,  and  yet  will  gi\e  a  workable  range  of  temperature 
for  reheating  to  a  uniform  color  at  temperatures  below  TOO". 

1st,  Highly  Huid  glasses  will  color  out  rapidly,  viscous 
glasses  slowly, 

2nd.  Keplacing  iime  with  either  lead  or  soda,  increiises  the 
rapidity  of  color  development,  lead  more  so  than  soda. 

3d.  High  SiO.  is  necessary  for  good  color,  low  SiO.  gives  a 
tendency  towards  brown  or  black,  and  opacity. 

•4th.  High  SiOo  (4.0  to  4.5  moL),  is  necessary  to  give  suffi- 
cient viscosity, 

5th,  With  high  silica,  lime-potash  glasses  the  tendency  to 
streakiness  increases.  Small  amounts  of  lead  reduce  streaki- 
ness. 

6th.  The  glass  giving  the  bast  color  in  series  B  is  No.  4. 
Glasses  Xos.  1,  2,  10  and  12  of  Series  C,  mo.st  nearly  approached 
the  requirements  of  a  good  ruby  glass.  They  could  all  be  poured 
without  the  color  developing,  and  on  reheating,  the  color  devel- 
oped at  favorable  temperatures.  Glasses  Xos.  6  and  8,  Series  C 
gave  the  most  transparent  colore. 

7th.  Iron  and  manganese  are  detrimental  to  a  good  red 
color. 

8th.  Remelting  improves  the  uniformity  of  the  color  which 
indicates  that  streakiness  is  due  to  lack  of  homogeneity. 

9th.  Density  of  color  is  apparently  increased  with  an  in- 
crease in  temperature.  Time  is  evidently  not  an  important  fac- 
tor in  this  case. 

DISCUSSION 

Pfof.  Silverman:  There  are  a  number  of  points  in  ^Mr. 
Williams'  paper  about  which  T  wish  to  inquire.  In  the  first 
place,  he  speaks  of  the  coloring  out  in  the  high-silica  copper  rub- 
ies. I  should  like  to  ask  whether  ]\lr.  Williams  found  any  direct 
bearing  by  the  alkali  content  of  the  glass.     There  is  a  claim 


22  DEVELOPMENT  OF  RUBY  COLOR  IN  GLASS 

made  at  i)resent  that  a  copper,  ruby  eaii  be  mauufactiired,  which 
is  a  ruby,  out  of  the  pot.  I  believe  his  views  correspond  with 
mine  iu  that  the  red  color  produced  is  due  to  high  alkali  in  the 
glass.  In  other  words,  the  glass  colors  out  while  cooling  in  the 
mold,  OT  even  earlier..  Then  as  to  tin  as  a  reducing  agent,  I  can 
corroborate  these  statements  also,  haidng  had  the  experience 
that  tin  alone  in  connection  with  copper  gives  a  rich  color,  while 
with  juanganese  and  iron  the  color  is  olf.  Tin  has  to  be  con- 
trolled very  carefully.  If  you  get  below  a  certain  point  you 
obtain  a  glass  which  does  not  color  sufficiently ;  and  if  you  go 
above  you  get  what  is  caLed  clouding  or  a  livery  color. 

I  would  like  to  ask,  to  what  'Sir.  AVilliams  attributes  lack  of 
uniformity  of. color;  and  wiiether  he  feels  that  a  melt  over  a 
short  duration,  like  thirty  minutes  could  give  a  homogeneous 
glass. 

Mr.  \Villia))is:  To  answer  the  last  (piestion  first:  the  uni- 
formity of  color  in  my  gla.sses  was  not  obtained  in  the  first  melt. 
There  were  signs  of  streakiiiess  at  first,  l)ut  u])()ii  remelting, 
good  clear  colors  wore  obtained.  It  is  probably  tlie  mechanical 
handling  of  the  glass,  or  the  duration  of  the  melt  which  has  a 
tendency  to  make  the  glass  cloudy  oi-  ch'ai-. 

The  first  ({uestiou  you  asked,  regarding  the  high  alkali  con- 
tent, I  did  not  quite  understaml,  however  I  will  make  this  point, 
that  when  I  used  lead,  replacing  the  alkali,  it  caiLsed  the  colors 
to  coine  out  move  (luickly  in  the  handling.  The  color  was  just 
as  good,  in  fact  a  little  better,  but  density  of  color  could  not  be 
controlled.  Lead  impi-oved  the  uniformity  of  the  color  but  gave 
a  tendency  toward  opacity.  If  you  do  not  want  the  color  to 
come  out  during  pressing,  it  is  necessary  to  keep  away  from  lead. 

Frof.  Silverman:  I  should  like  to  know  further,  what  the 
object  is  in  trying  to  prevent  the  coloi-  from  coming  out  during 
pressing. 

Mr.  Williams:  If  you  do  not  prevent  it,  the  different  var- 
iations in  the  cooling  of  the  mold  wouhl  not  uive  the  same  shad- 
ing of  red  in  the  finished  pieces. 

Prof.  Silverman:  But  do  you  not  get,  the  same  effect  by 
heating  to  a  certain  temperature  afterwards? 


DEVELOPMENT    OK    KIHV    COLOH     IX    GLASS  23 

Mr.  Williaiii^:  W's:  hut  (•;in  ynu  cunt  ml  I  lie  i-;iti'  ol'  codliiii;' 
of  glass  ill  th('  iiidlil  .siit'liciciili}-  ;ii'(Mii'iitcly  as  to  L^-ivc  iinit'dniiity 
of  color  from  piece  to  piece .' 

Prof.  Silvcn)i(ni :  T  cannot  (iiiilc  sec  how  that  has  a  beariiiu' 
on  the  rate  of  cooliiiii'.  Suppose  your  i^'lass  does  not  color  out 
below  7(XV\  You  uiiuht  have  a  mold  nuywlici'c  fi-om  400  1o 
(iOO.  and  the  fact  lliat  ndu  have  no  coloi'  wouhl  he  no  indication 
that  your  mold  tempcratui'e  is  correct.  In  othei-  words,  you 
have  such  a  large  range  below  the  coloring-out  temperature  that 
it  does  not  seem  any  better  indication  as  to  mold  temperature, 
than  if  you  had  a  glass  that  colored  out,  except  possibly  to  tel! 
you  that  the  mold  is  too  hot. 

Mr.  Williarns:  ]\Iy  experience  with  glass  that  colored  out 
was  that  glass  of  various  thicknesses  was  different  in  shade.  The 
difference  in  temperature  of  a  mold  would  influence  the  coh)r. 
The  coloring  out  at  a  definite  temperature  also  depends  upon 
the  speed  at  which  a  glass  cools  through  the  small  temperature 
range  of  color  development.  If  the  glass  cools  at  a  high  rate  of 
speed  through  this  temperature,  the  colloidal  copper  would  not 
come  out  in  large  enough  particles  to  show  color.  If  the  cooling 
rate  is  slower  the  particles  grow  of  sufficient  size  to  give  color. 

Mr.  GeUiharp:  I  should  like  to  ask  whether  that  was  not 
sub-oxide  of  copper. 

Mr.  Williams:     I  used  cuprous  oxide. 

Prof.  StuII:  Perhaps  I  mig-ht  throw  a  little  light  on  Prof. 
Silverman's  question  by  stating,  that  airoug  the  things  "Sir.  Wil- 
liams is  investigating  is  a  study  of  the  temperatures  at  which 
the  copper  ruby  comes  out,  and  the  effect  of  length  of  time  as 
well  as  temperature  in  bringing  it  out.  That  is  why  he  is  trying 
to  secure  colorless  glass  to  liegin  with. 


